Bottles for culturing of blood for the presence of microorganism and related instruments for analyzing such bottles in a noninvasive manner are known in the art and described in the patent literature. See U.S. Pat. Nos. 5,858,769; 5,795,773; 4,945,060; 5,094,955; 5,164,796; 5,217,876; and 5,856,175. The bottles and instruments of the above-listed patents have been commercialized with success by the present assignee under the trademark BacT/ALERT.
The bottles described in these blood culture instruments utilize colorimetric sensors placed in the bottom of the bottle and in contact with the sample media to determine the presence/absence of bacterial growth. Once a clinical/industry sample is added to the liquid growth media present in the bottle and incubation occurs, the concentration of carbon dioxide increases as the number of microorganisms increase; carbon dioxide is a respiration by-product of bacterial growth. Alternatively, changes to the media pH that are related to the growth of microorganisms can also be monitored by the sensor. The basic operation of the BacT/ALERT sensor and monitoring electronics is described in U.S. Pat. No. 4,945,060 and also in an article by Thorpe et al. in “BacT/Alert: an Automated Colorimetric Microbial Detection System,” which was published in the Journal of Clinical Microbiology, July 1990, pp. 1608-12. The '060 patent and the Thorpe et al. article are incorporated by reference here.
While the BacT/ALERT sensing system is robust and has been used in blood culture systems successfully for many years, it does have a few areas for improvement. For example, the BacT/ALERT system identifies a positive culture but does not provide information on whether the microorganism in the culture is resistant to antimicrobial treatment. Further, the BacT/ALERT system was not designed to facilitate immediate processing of a positive bottle, and the cumulative time required to manually remove a positive bottle and subculture its contents to prepare a log phase microbial suspension for testing significantly delays identification of the antimicrobial resistance status of the sample. However, a new blood culture system soon to be launched commercially has capability to automatically unload a positive bottle and transfer it to an adjacent instrument for processing. Microbial cells, already in logarithmic growth phase at time of detection by the continuously monitoring culture system, may be immediately and automatically transferred to the device of this invention under controlled conditions that greatly minimize any lag phase in growth of the subculture.
There is a long-felt but unmet clinical need to have a device and method for identifying antimicrobial resistance in a microorganism directly from a positive blood culture bottle within a few hours of detection. The device of the current invention has the capability to meet this need by minimizing any manipulation-induced lag in microbial growth upon subculture through timely, controlled and automated processing of a positive bottle, and by continuously monitoring the optical density of said subcultures.